Polyolefin resins such as polyethylene and polypropylene and polyester resins as represented by a polyethylene terephthalate have excellent properties such as formability, transparency, mechanical strength and resistance against chemicals and have, therefore, been used as packing materials such as films, sheets and bottles in a variety of fields.
The EVOH copolymer (saponified product of an ethylene-vinyl acetate copolymer of a saponification degree close to 100%) has been known as a resin having excellent oxygen-barrier property. In the field of packing materials, in particular, there have been widely used multilayered structures using the polyolefin resin or the polyester resin as the inner and outer layers and using the EVOH copolymer as the intermediate layer (oxygen-barrier layer).
In recent years, further, as a structure having excellent oxygen barrier property, there has also been put into practical use a multilayered structure having, as an intermediate layer (oxygen-barrier layer), a layer of an oxygen-absorbing resin obtained by dispersing, in the EVOH copolymer, the oxygen-absorbing components inclusive of an oxidizing organic component of an unsaturated group-containing ethylene-based polymer (e.g., polybutadiene, etc.) and a transition metal catalytic component such as iron or cobalt between the inner and outer layers (e.g., see patent document 1).
Here, despite of its excellent oxygen-barrier property, the EVOH copolymer has poor adhesive property to other resins. Therefore, it is necessary to form an adhesive layer neighboring the layer that contains the EVOH copolymer. Referring, for example, to the multilayered structure having an oxygen-absorbing resin layer proposed in the patent document 1, the EVOH copolymer is used as a resin base member of the oxygen-absorbing resin layer and, besides, the layers of the EVOH copolymer are formed on both sides of the oxygen-absorbing resin layer in order to compensate for a decrease in the oxygen-absorbing capability (decrease in the oxygen-barrier property) due to the aging of the oxygen-absorbing resin layer. Here, the layer of the EVOH copolymer has been adhered to the inner and outer layers via adhesive layers. To utilize the EVOH copolymer as described above, it is necessary to form adhesive layers which are not really necessary for improving the function of the packing materials causing, therefore, the layer structure to become complex and, besides, necessitating an extruder for forming the adhesive layers resulting in an increase in the cost of production. Therefore, it has been urged to improve the above problems.
As a packing material that solves the above problems, a patent document 2 proposes a multilayered structure having an intermediate layer of a blend of the EVOH copolymer and the polyester resin.